They don't really have an incentive to spell it out, in detail. I did a quick patent search, but didn't find anything obvious.
Here's a QD-OLED explainer, I found.
QD-OLED technology delivers the kind of TV picture quality we’ve been dreaming about for years. Here’s everything you need to know about QD-OLEDs.
www.digitaltrends.com
It goes into lots of details that aren't necessarily relevant to QD-OLED, but there's a part near the end which could reveal some of the challenges:
Having your (OLED) cake and eating it, too
Blue OLED material — the light source of QD-OLED displays — is a notoriously tricky substance to work with.
Much like other OLED materials, there’s a three-way trade-off between lifespan, brightness, and efficiency. Generally speaking, any time you prioritize one of these attributes, the other two suffer. Drive an OLED pixel hard enough to produce the brightness you want and you not only diminish its life expectancy but also its efficiency.
But QD-OLED displays may prove to be the exception to this rule. By using three layers of blue OLED material per pixel, each layer can share the brightness burden.
My guess is that it might have something to do with how to balance the distribute current between the layers, and/or things like balancing overdrive vs. panel life, etc.